Alzheimer's Disease (AD) is a degenerative brain disorder characterized clinically by progressive loss of memory, cognition, reasoning, judgment and emotional stability that gradually leads to profound mental deterioration and ultimately death. AD is a common cause of progressive mental failure (dementia) in aged humans and is believed to represent the fourth most common medical cause of death in the United States. AD has been observed in varied races and ethnic groups worldwide and presents a major present and future public health problem. The disease is currently estimated to affect about two to three million individuals in the United States alone. To date, AD has proven to be incurable.
The brains of individuals with AD exhibit neuronal degeneration and characteristic lesions variously referred to as amyloidogenic plaques, vascular amyloid angiopathy, and neurofibrillary tangles. Large numbers of these lesions, particularly amyloidogenic plaques and neurofibrillary tangles, are generally found in several areas of the human brain important for memory and cognitive function in patients with AD. Smaller numbers of these lesions in a more restricted anatomical distribution are found in the brains of most aged humans who do not have clinical AD. Amyloidogenic plaques and vascular amyloid angiopathy also characterize the brains of individuals with Trisomy 21 (Down's Syndrome) and Hereditary Cerebral Hemorrhage with Amyloidosis of the Dutch-Type (HCHWA-D). At present, a definitive diagnosis of AD usually requires observing the aforementioned lesions in the brain tissue of patients who have died with the disease or, rarely, in small biopsied samples of brain tissue taken during an invasive neurosurgical procedure.
Several lines of evidence indicate that progressive cerebral deposition of particular amyloidogenic proteins, .beta.-amyloid proteins, (.beta.AP), play a seminal role in the pathogenesis of AD and can precede cognitive symptoms by years or decades. See, Selkoe, (1991) Neuron 6:487. Recently, it has been shown that .beta.AP is released from neuronal cells grown in culture and is present in cerebrospinal fluid (CSF) of both normal individuals and AD patients. See, Seubert et al., (1992) Nature 359:325-327.
A possible correlation to the plaque pathology has been developed by several groups demonstrating the direct .beta.AP neurotoxicity toward, cultured neurons. Direct neurotoxicity of .beta.AP was recently reported to be attenuated by co-treatment with TGF-.beta. (Chao et al., Soc. Neurosci. Abs., 19:1251 (1993)).
More recently, in addition to the direct neurotoxicity, an inflammatory response in the AD brain, perhaps elicited by .beta.AP, also contributes to the pathology of the disease. A limited clinical trial with the NSAID indomethacin exhibited a retardation in the progression of Alzheimer's dementia (Rogers et al., Science, 260:1719-1720 (1993)).
Despite the progress that has been made in understanding the underlying mechanisms of AD, there remains a need to develop compositions and methods for treatment of these diseases. Treatment methods could advantageously be based on drugs which are capable of increasing TGF-.beta. expression in the brain, thus ameliorating the .beta.-amyloid peptide mediated neurotoxicity and inflammatory response associated with AD.